CN110079004B - 220kv rated voltage ultra-clean ultra-smooth semi-conductive shielding material and preparation method thereof - Google Patents

Abstract

The invention provides an ultra-clean ultra-smooth semi-conductive shielding material with 220kv rated voltage, which comprises the following components: 78-45 parts of EBA or EEA40, 16.5-21.5 parts of functional polyolefin, 30-37 parts of clean special carbon black, 1.7-3.2 parts of lubricant, 0.3-0.5 part of antioxidant and 1-2 parts of cross-linking agent. The prepared 220kv semiconductive shielding material has good heat resistance, clean surface without bulge and excellent conductivity.

Description

220kv rated voltage ultra-clean ultra-smooth semi-conductive shielding material and preparation method thereof

Technical Field

The invention belongs to the field of crosslinked polyethylene insulated cable semiconductive shielding materials, and particularly relates to an ultra-clean ultra-smooth semiconductive shielding material with a rated voltage of 220kv and a preparation method thereof.

Background

At present, because the domestic semiconductive shielding material is limited by factors such as raw material selection, process control, processing equipment and the like, the domestic semiconductive shielding material can only meet the market demand of supplying the semiconductive shielding material with rated voltage of 35kv or below.

In the production of domestic semiconductive shielding materials with the voltage of 35kv or below, EVA, high-structure conductive carbon black and white oil with proper melt index are generally adopted as main raw materials, and an antioxidant, a release agent, a cross-linking agent and other auxiliary agents are supplemented. An internal mixer is mainly used as mixing processing equipment, and the semiconductive shielding material is prepared through the process steps of internal mixing, extrusion granulation, dehydration, screening, dry air conveying, high mixing and the like.

In the cable manufacturing process, the maximum heating temperature of the shielding material in the vulcanization pipe is 260-. EVA is selected as the base material of the semiconductive shielding material with the temperature of 35kv or below, the EVA has more heating weight loss than EBA and EEA at the temperature of 260 ℃, and the high-temperature stability of the EVA is inferior to that of the EBA and the EEA.

The traditional 35kv and below semiconductive shielding material selects conductive carbon black which is generally domestic furnace carbon black, has general conductivity and more impurities, and can not meet the requirements of 220kv and above semiconductive shielding material on electrical property and cleanness.

The preparation of the traditional anti-oxidation-crosslinking system of the semiconductive shielding material can not meet the requirement of long-term low linear velocity production of 220kv cables. In general, the conventional single antioxidant is used for the semiconductive shielding material, and DCP is used as a crosslinking agent, and the DCP can be rapidly decomposed at the temperature of more than 120 ℃ to promote crosslinking, so that the extrusion safety of the shielding material is poor. This is extremely unsafe for 220kv cables that require low speed, long term production, and are prone to the development of old glue.

The traditional 35kv and below outer shielding material is not tightly combined with insulation because of selecting high VA content EVA, and the outer shielding can be peeled off. On the cable with 220kv or even higher voltage level of alternating voltage, the close connection of shielding and insulation on the microscopic level must be achieved, otherwise the service life of the cable is seriously affected, the outer screen is not strippable, otherwise the safety of the cable in long-term operation is affected.

The conductive carbon black in the shielding material is difficult to disperse completely and uniformly by adopting an internal mixer for production, and the requirement of ultra-clean and ultra-smooth surface of the shielding material of the 220kv cable cannot be met.

Disclosure of Invention

Aiming at the problems, the invention provides an ultra-clean ultra-smooth semi-conductive shielding material with the rated voltage of 220 kv.

In order to achieve the purpose of the invention, the technical scheme adopted by the invention is as follows:

an ultra-clean ultra-smooth semi-conductive shielding material with a rated voltage of 220kv, which is characterized by comprising: 78-45 parts of EBA or EEA40, 16.5-21.5 parts of functional polyolefin, 30-37 parts of clean special carbon black, 1.7-3.2 parts of lubricant, 0.3-0.5 part of antioxidant and 1-2 parts of cross-linking agent.

Further, the melt index range of the EEA or the EBA is 12-15g/10min, and the number of crystal points is less than 5.

Further, the functional polyolefin is metallocene LLDPE or LDPE, the melt index range of the metallocene LLDPE or LDPE is 3-4g/10min, and the number of crystal points is less than 5.

Further, the EA monomer content or BA monomer content in the EEA or EBA is 18-22%.

Further, the clean special carbon black has a DBP absorption value of 160ml/100g, an ash content of less than 0.2%, a heating loss of less than 0.2%, a 325-mesh residue content of less than 10ppm, a sulfur content of less than 0.2% and a moisture content of less than 200 ppm.

Further, the lubricant is at least one of silicone master batch, cracking PE wax, ethylene bis stearamide and oleamide; the silicone master batch is white particles, the particle size is 3 x 4 x 3mm, and the effective component is 50%; the molecular weight of the cracking PE wax is 4500, and the melting distance is 105-115; the molecular weight of the ethylene distearate amide is 593, and the melting point is 143-146 ℃; the molecular weight of the oleamide is 281.48, and the melting point is 72-77 ℃.

Further, the antioxidant is a compound mixture of 300#, 1010# and TBHQ; the molecular weight of the 300# is 358.54, the melting point is 161-164 ℃, and the purity is more than 98 percent; the molecular weight of the 1010# is 1177.63, the melting point is 110-125 ℃, and the purity is more than 98 percent; the molecular weight of the TBHQ is 166.22, the melting point is 126.5-128.5 ℃, and the purity is more than 98%.

Further, the crosslinking agent is BIBP or a bis 25 vulcanizing agent; the molecular weight of BIBP is 338, the melting point range is 46-52 ℃, and the purity is more than 96%; the molecular weight of the bis-25 vulcanizing agent is 290.44, the melting point is 8 ℃, and the purity is more than 95 percent.

A preparation method of an ultra-clean ultra-smooth semi-conductive shielding material with a rated voltage of 220kv is characterized by comprising the following steps:

(1) feeding, namely feeding EBA or EEA, clean special conductive carbon black, a lubricant and an antioxidant according to a specified feeding port to prevent foreign impurities from entering;

(2) setting a formula, feeding by a weightlessness type metering scale according to a formula proportion, and mixing and processing by a reciprocating machine, wherein the reciprocating machine is a four-pin type reciprocating machine, the length-diameter ratio of the reciprocating machine is 17.5:1, and the discharging temperature is 200-220 ℃;

(3) extruding and granulating, wherein a 300-mesh 4-layer strong filtering process is additionally arranged at a single screw machine head in the process to intercept physical impurities and ensure the smoothness of cable extrusion;

(4) dehydrating, screening and drying, and finally controlling the water content to be less than 200 ppm;

(5) blowing to a high-speed mixer, controlling the feeding temperature to be 40-42 ℃, adding the cross-linking agent, and mixing at high speed until the particle temperature reaches 53-55 ℃ so as to fully absorb the cross-linking agent;

(6) and (3) dust screening treatment, namely adding the particles subjected to high mixing into a blast vibration screen, carrying out powder screening treatment, and removing the powder subjected to high mixing. The above process is cycled for 3 times to achieve the best dust removal effect.

The invention has the beneficial effects that: EBA or EEA is used as a base material, so that the heat resistance of the system and the lower limit of the thermal decomposition temperature of the base material are improved. The EBA and EEA have good processability. The EBA thermal decomposition temperature is 330 ℃, the EEA thermal decomposition temperature is 350 ℃, and both the EBA thermal decomposition temperature and the EEA thermal decomposition temperature are far higher than 240 ℃ of the EVA; the extrusion processing temperature of the two can be as high as 300 ℃ and higher than 220 ℃ of EVA. The cable can pass through a vulcanizing pipe with the temperature as high as 270 ℃ in the manufacturing process, and EBA or EEA is selected to reduce the thermal decomposition of the base material to the maximum extent and prolong the service life of the high-voltage cable. The melt index range is 12-15g/10min, the basic fluidity of the system is ensured, the extrusion requirement of the shielding material can be met only by adding a small amount of lubricant, the generation of residues of a vulcanization pipe in the production and manufacturing process of the high-voltage cable is reduced, and the pollution discharge times of the vulcanization pipe are reduced.

The ultra-smooth cable is ensured when the number of the matrix resin crystal points is very small, and no bulge with the size of more than 75 mu m is arranged on the surface of the outer screen.

And clean carbon black is used to ensure the conductivity and cleanness of the system. The largest source of impurities in the screen stock is carbon black. The high oil absorption value ensures that the conductivity of the system is excellent, the low content of ash and 325-mesh residues ensure the cleanness of the carbon black, and the low sulfur content can reduce the influence of the inner and outer screens on the color change of conductors and cable copper strips. Further ensuring the cleanness of the whole 220kv shielding material.

The functional polyolefin fused in a specific range is used for adjusting the fluidity of a system, adjusting the polarity of a formula system and improving the cohesiveness of shielding and insulation, so that the inseparable outer screen and insulation and the tight combination of the inner screen and insulation are really realized. The best technical effect can be achieved by a certain range of melt index EEA or EBA and a specific range of melt index functional polyolefin, if the melt index of EEA or EBA is not in the range of 12-15g/10min, the specific technical effect can not be achieved by the invention according to the results of the examples.

The compound antioxidant is adopted, the addition amount is increased, and the crosslinking agent bis 25 or BIBP with higher decomposition temperature is selected, so that a certain crosslinking degree of a system is ensured, too high crosslinking degree of the system is avoided, the extrusion safety of the system is improved, and the condition of extruding the 'old rubber' in the long-term production of the high-voltage cable is reduced to the maximum extent.

The reciprocating type extrusion granulation processing equipment is adopted for production, materials are automatically metered according to the formula, and the formula misalignment caused by human factors is reduced. Meanwhile, the complete dispersion of the carbon black can be realized in the production of the reciprocating machine, and the prepared shielding material can meet the requirement of ultra-clean and ultra-smooth. The length-diameter ratio of the used reciprocating engine is 17.5:1, and the length-diameter ratio can ensure that the carbon black in the formula is fully dispersed.

And a 300-mesh 4-layer strong filtering process is adopted, so that the entering of physical impurities is maximally reduced. Maximizing the cleaning degree of the lifting system.

And a dust screening treatment process is added at the end of the production process, the process is circulated for 3 times, and the experimental calculation can reduce 99% of powder after high mixing. These powders contain a large amount of cross-linking agent, which is very likely to cause the extrusion of the gel during the cable manufacturing process. The process can avoid the possibility of glue aging during the production of the 220kv high-voltage cable, and improves the extrusion safety of the cable production.

The prepared 220kv ultra-clean ultra-smooth semi-conductive shielding material has good heat resistance and little thermal decomposition during cable manufacturing.

The volume resistivity of the product at 20 ℃ is about 20 omega cm, and is lower than 35kv and below.

The product is tested by testing a sample with the total surface area of 1m2, the height of the surface protrusions is 50-75 μm, the number of the surface protrusions is less than or equal to 5, and the number of the surface protrusions greater than 75 μm is 0.

Drawings

Fig. 1 is a schematic diagram of an optical scanning device with a high resolution camera.

Detailed Description

The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Any modifications that can be easily made by a person skilled in the art to the present invention without departing from the technical solutions of the present invention will fall within the scope of the claims of the present invention.

Example 1

45 parts of EBA, 45 parts of B28N230 (the melt index is 14 g/min), 18 parts of metallocene LLDPE, 15 parts of VXC72#, 19 parts of Czech B type carbon black (cleaning type carbon black), 0.4 part of silicone master batch, 0.7 part of pyrolysis PE wax, 0.8 part of ethylene bis stearamide, 0.5 part of oleamide, 0.3 part of antioxidant 300#, 0.2 part of antioxidant 1010# and 0.1 part of antioxidant TBHQ. BIBP is adopted as crosslinking agent, and the addition amount is 1-1.2 parts

The matrix resin is EBA, B28N230, the melt index is 14g/10min, the number of crystal points is greater than 100 mu m, and the number of crystal points is 1200cm²) Is less than 3. The BA monomer content was 18%.

The melt index of the metallocene LLDPE is 3.2g/10min, and the number of crystal points is more than 100 mu m and more than 1200cm²) Is less than 3.

The VXC72 carbon black has a DBP absorption value of 130ml/100g, an ash content of 0.15%, a heating loss of 0.13%, a 325-mesh screen residue content of 5ppm, a sulfur content of 0.1% and a moisture content of 153 ppm.

The DBP absorption value of the Czech B-type carbon black is 153ml/100g, the ash content is 0.1 percent, the heating decrement is 0.1 percent, the content of 325-mesh screen residue is 7ppm, the sulfur content is 0.1 percent, and the water content is 140 ppm.

Example 2

42 parts of EBA, 42 parts of E1770 (the melt index is 12 g/min), 2102, 20 parts of LDPE, 20 parts of VXC72#, 14 parts of Czech B-type carbon black, 2 parts of cracking PE wax, 0.6 part of oleamide, 0.9 part of ethylene bis stearamide, 0.4 part of antioxidant 300#, and 0.1 part of antioxidant 1010 #. The cross-linking agent adopts bis-25, and the addition amount is 1-1.2 parts.

The matrix resin used was EBA, E1770, with a melt index of 14g/10min, the number of crystal points (> 100 μm, pieces/1200 cm)²) Is less than 3. The BA monomer content was 20%.

The LDPE2102 has the melt index of 3.5g/10min and the number of crystal points (> 100 mu m, one/1200 cm)²) Is less than 3.

Comparative example 1

The same as example 1 except that thiobis phenolic antioxidants were used instead of the built antioxidant system (antioxidant # 300, antioxidant 1010, antioxidant TBHQ).

Comparative example 2

Same as example 1 except that antioxidant No. 300 was used alone.

Comparative example 3

Same as example 1 except that antioxidant 1010 was used alone.

Comparative example 4

Same as example 1 except that TBHQ, an antioxidant, was used alone.

Comparative example 5

The EBA addition was 63 parts as in example 1, except that no metallocene LLDPE was added.

Comparative example 6

The same as in example 1, except that a superconducting carbon black (DPB absorption value of 310ml/100g, primary particle diameter of 40nm, total ion content < 60ppm, moisture < 100 ppm) was used in place of the carbon black of the present invention.

Comparative example 7

The same as example 1 except that VXC72#34 parts was used, no Czech type B carbon black was used.

Comparative example 8

Same as example 1 except that 34 parts of czech type B carbon black was used, VXC72# was not used.

Comparative example 9

Same as example 1, except that EBA (melt index 10 g/min) was used.

The materials of the examples and comparative examples were tested.

The smoothness of the product is detected by a laser scanner produced by German OCS company, the principle is that a 220kv semiconductive shielding material is extruded out of a strip-shaped sheet, in the continuous extrusion process, the scanner emits light waves to emit to the surface of the sheet, and if the light waves touch a protruding point, the height and the size of the sheet are automatically calculated by the instrument.

The following method for measuring the size and quantity of surface protrusions

The test method is suitable for testing the size and the quantity of the protrusions on the surface of the semiconductive shielding material for the 220kv cable. The test method is a test carried out under an optical scanning device with a high-resolution camera, the scanning speed and the lowest height scanned by the device, the surface of the sample strip is scanned by the high-resolution camera, and the principle of the device is shown in figure 1.

Test method

1. The test should be carried out in a standard state of (23 + -2) deg.C and relative humidity of (50 + -5)% and the time for which the equipment is adjusted in the standard state should be not less than 6 h.

2. And adjusting the temperature of each temperature zone of the extruder to ensure that the extruded material reaches a good plasticizing state for testing, and adjusting the thickness of the sample belt to the optimal measurement thickness, wherein the detection sensitivity of the device is not lower than 85%.

3. The test was started after the extruded sample had stabilized thickness and the total surface area of the test specimens was 1m 2.

4. Test result processing

Characterization of the size and quantity of surface protrusions to test the total surface area 1m²The sample of (4), recording surface protrusions having a height of 50 to 75 μm and a number greater than 75 μm.

TABLE 1

As is clear from the data in Table 1, examples 1 and 2 are excellent in mechanical properties and aging resistance, and have proper heat elongation, which indicates that the degree of crosslinking is sufficient but not too high. The volume resistivity was low, indicating that examples 1 and 2 have good electrical conductivity. The number of surface protrusions is 0, which indicates that the carbon black is completely dispersed in the system. Non-strippable also indicates that examples 1 and 2 have reasonable base material types and ratios, good carbon black dispersion, and good adhesion to insulation.

TABLE 2

From Table 2, it is seen that comparative examples 1, 2, 3 and 4 show that the use of a single antioxidant provides excellent hot elongation data, the degree of crosslinking is too high, the tensile strength is improved, the elongation at break is reduced, and the product is not resistant to aging. Too high a degree of crosslinking even affects the electrical properties of the article, since the system is too crosslinked, destroying the conductive paths to some extent.

The data demonstrate the rationality of selecting a compounded antioxidant.

In contrast, comparative example 5, which uses only EBA, showed a significant decrease in strength and a slight increase in elongation. The ageing resistance is general. However, the article was peelable from the insulation, indicating that comparative example 5 did not bond well to the insulation.

TABLE 3

As is clear from Table 3, comparative examples 6, 7 and 8, in which a single type of carbon black was used, were difficult to disperse, had poor mechanical properties, had significantly higher volume resistance than those of examples 1 and 2, had many surface projections due to poor dispersion of the carbon black, had poor adhesion to insulation, and were peelable.

Comparative example 9 using EBA with an unreasonable range of melt index, the strength was reduced, the volume resistivity was also large, and the article still peeled from the insulation with a small amount of protrusions on the surface.

In conclusion, the examples 1 and 2 completely meet the requirements of the 220kv ultra-clean ultra-smooth semi-conductive shielding material.

Claims (5)

1. An ultra-clean ultra-smooth semi-conductive shielding material with a rated voltage of 220kv, which is characterized by comprising: 78-45 parts of EBA or EEA40, 16.5-21.5 parts of functional polyolefin, 34 parts of clean special-conductive carbon black, 1.7-3.2 parts of lubricant, 0.3-0.5 part of antioxidant and 1-2 parts of cross-linking agent;

the melt index range of the EEA or the EBA is 12-15g/10min, and the number of crystal points is less than 5;

the functional polyolefin is metallocene LLDPE or LDPE, the melt index range of the metallocene LLDPE or LDPE is 3-4g/10min, and the number of crystal points is less than 5;

the clean type special carbon black is 15 parts of VXC72# and 19 parts of Czech type B carbon black, or the clean type special carbon black is 20 parts of VXC72# and 14 parts of Czech type B carbon black;

the antioxidant is a compound mixture of 300#, 1010# and TBHQ; the molecular weight of the 300# is 358.54, the melting point is 161-164 ℃, and the purity is more than 98 percent; the molecular weight of the 1010# is 1177.63, the melting point is 110-125 ℃, and the purity is more than 98 percent; the molecular weight of the TBHQ is 166.22, the melting point is 126.5-128.5 ℃, and the purity is more than 98%.

2. The ultra-clean ultra-smooth semi-conductive shielding material with 220kv rated voltage according to claim 1, characterized in that: the content of EA monomer or BA monomer in the EEA or EBA is 18-22%.

3. The ultra-clean ultra-smooth semi-conductive shielding material with 220kv rated voltage according to claim 1, characterized in that: the lubricant is at least one of silicone master batch, cracking PE wax, ethylene bis-stearic acid amide and oleic acid amide; the silicone master batch is white particles, the particle size is 3 x 4 x 3mm, and the effective component is 50%; the molecular weight of the cracking PE wax is 4500, and the melting distance is 105-115; the molecular weight of the ethylene distearate amide is 593, and the melting point is 143-146 ℃; the molecular weight of the oleamide is 281.48, and the melting point is 72-77 ℃.

4. The ultra-clean ultra-smooth semi-conductive shielding material with 220kv rated voltage according to claim 1, characterized in that: the cross-linking agent is BIBP or a bis 25 vulcanizing agent; the molecular weight of BIBP is 338, the melting point range is 46-52 ℃, and the purity is more than 96%; the molecular weight of the bis-25 vulcanizing agent is 290.44, the melting point is 8 ℃, and the purity is more than 95 percent.

5. The method for preparing the ultra-clean ultra-smooth semi-conductive shielding material with the rated voltage of 220kv according to claim 1, which is characterized by comprising the following steps:

(1) feeding, namely feeding EBA or EEA, clean special conductive carbon black, a lubricant and an antioxidant according to a specified feeding port to prevent foreign impurities from entering;

(2) setting a formula, feeding by a weightlessness type metering scale according to a formula proportion, and mixing and processing by a reciprocating machine, wherein the reciprocating machine is a four-pin type reciprocating machine, the length-diameter ratio of the reciprocating machine is 17.5:1, and the discharging temperature is 200-220 ℃;

(3) extruding and granulating, wherein a 300-mesh 4-layer strong filtering process is additionally arranged at a single-screw machine head in the process to intercept physical impurities and ensure the smoothness of cable extrusion;

(4) dehydrating, screening and drying, and finally controlling the water content to be less than 200 ppm;

(5) blowing to a high-speed mixer, controlling the feeding temperature to be 40-42 ℃, adding the cross-linking agent, and mixing at high speed until the particle temperature reaches 53-55 ℃ so as to fully absorb the cross-linking agent;

(6) dust screening treatment, namely adding the particles subjected to high mixing into a blast vibration screen for powder screening treatment, and removing the powder subjected to high mixing; the dust screening process is circulated for 3 times.

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